What's the highest temperature any of you have had on a diacetyl rest making a lager or a clean ale? Anyone ever had one go into the mid-70s? If so, any issues with flavor profile? I know ideal is at 68 deg F, but wondering if higher might not be so detrimental. I kinda lost control of temperature on one of my, uh, 5 gallon batches. The beer was maybe 6 points away from terminal when it happened. Thanks.
I had a lager rise up to 78˚F during a power failure over a period of three or four days and it was still fine. I'm guessing that once you're past primary fermentation and into secondary you're pretty good to go as long as the yeast doesn't start to die off.
I haven't gone much above 68F, but my best guess would be that the only consequence would be accelerated aging. Hopefully not too much during the time it takes to clean up the diacetyl. It would be terrible to have to dump a, uh, 5 gallon batch. Another thought... are you detecting diacetyl, or is this an insurance rest? If the latter, I wonder if the runaway temp might (assuming it was higher and not lower than intended) have already served as the rest. 6 points away from terminal wouldn't be a completely crazy place to start ramping up to a rest.
I've done d rests at 70f multiple times on multiple lagers. Although I detected no Diacetyl in those beers.
The beer has minimal hop character, and most of my *friends* consume the beer fairly quickly, so not too worried about aging. Even on ales, I do conduct a bit of a rest - when 1 -2 deg P away from terminal gravity, I turn off the temp control and let the temp free rise a few degrees, then maintain at that temp at terminal gravity for 1-2 days until I am sure diacetyl is gone. I don't ever let it get above 68 though. I'll be sure to make sure diacetyl is free from this batch as well, hoping based on this feedback it will be fine. Thanks, as always.
I don't think higher 70s would be an issue either. I tend to only keep my lagers "cold" for 4-7 days then let em warm to room temp. Love me some quick lager.
Once the primary cursory bi-products (or lack there of) are created in the first few days of fermentation there shouldn't be any issue with an elevated temp. I could see too long at that temp leading to staling issues, or if in a large conical filled with barrels of beer with an unjacketed cone you could have accelerated autolysis.
FWIW, I did a very accidental diacetyl rest at a way too high temp. I had a Czech Pils that I did not do a rest with that ended up as a disgusting buttery mess once it was in the keg (never sampled in the fermenter), a long lagering period did not help, so I ended up just pulling the keg and leaving it in my garage for the whole summer (probably hit upper 90s). Finally needed some kegs, but before dumping that one, I decided to put back in the kegerator and see what happened with the beer. The diacetyl was gone and the beer was absolutely drinkable, ended up killing that keg at the labor day pool party. TL;DR I wouldn't dump that "5 gallon batch" without tasting it first
